The ice on Lake Michigan has turned blue. Here's why.

The ice on portions of Michigan's Great Lakes has turned blue, but don't worry, there's a perfectly good reason why.

The phenomenon is common on glaciers, but not so much on large swathes of lake ice. It's happening where Lake Michigan meets Lake Huron, at a place called the Straits of Mackinac. There, fat slabs and mounds of cracked blue ice have collected near the shorelines.

The ice, however, is not actually turning blue. The color is a result of the way sunlight is bouncing off this particular ice, explained Ted Scambos, a research scientist at the National Snow and Ice Data Center, in an interview.

Sometimes, weather conditions — such as a lack of high winds — allow water to freeze slowly and evenly, resulting in ice composed of large crystals (unlike snow, which is formed quickly and made up of small crystals).

When light hits these big ice crystals, it can travel deep into the structures (compare this to snow, wherein light hits a sharp edge and reflects off of it right away, resulting in blinding white). When the light travels deeper into slowly formed ice, some of the red wavelengths of sunlight — which is the longest wavelength of visible light — get absorbed into the ice structure.

The blue, which is the shortest wavelength of visible light, bounces back out, meet our eyes, and results in a deep aqua color.

Sunlight reflecting off the Thwaites glacier in Antarctica, which makes the water look an aqua color.

Image: nasa

But this isn't the complete story. Blue ice is also composed of relatively pure, untainted water, which allows the blue reflection to be so vivid and dominant.

"It's a tribute to how clean the upper surface of Lake Michigan is," said Scambos, adding, "At least somewhere in Lake Michigan."

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